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Posted by David Delaney on October 8, 2003, 3:47 am
 
On 7 Oct 2003 22:00:22 -0400,
nick@acadia.ee.vill.edu (Nick Pine) wrote:


Yes. Hence my interest in shelf-stacked 5 gallon
pails or some better mass/glass surface ratio
thermal mass.

I'd rather depend on ceiling fans for distribution
than on fans and/or dampers for collection.

1) House on level ground. Thermal mass overhead
and completely above the collector, but not above
the interior ceiling. E.g. a high ceiling bungalo
in which the living room, kitchen, and other
common spaces have a common ceiling. The common
ceiling is just above the thermal mass, which
heats the ceiling and upper walls down to the
level of the bottom of the thermal mass. A
low-power high-cfm push-down ceiling fan provides
controlled downward heat distribution. If the fan
fails, radiation from the convectively heated
ceiling and upper walls keeps the house livable.
(And two such fans with independent controls, and
even power supplies, could be provided reasonably
cheaply.)

2) House built on an earth platform jutting from a
south facing slope, allowing the collector to be
below the thermal mass and the living space, which
are on the same level. Living space heated
entirely by natural convection, perhaps with the
assistance of convenient but not essential fans
and controls.


In a purpose-built house, the mass can straddle
the south wall, being half over the sun space and
half over the house interior. Easy structural
design. People get used to living with many floors
of an apartment building above them.

A better question would be, "For a given heat
content would you rather have a stratified or
unstratified store?"  

So sunspaces with thermal mass are a good idea?
:-)) I'm joking. I'm joking.


One of the beauties of the Cliff House is that
that a thin film of hot air rises close to the
absorber and is separated from the glazing by the
descending cool air from the bottom of the
(stratified) thermal mass. This descending air is
at the temperature of the top of the living space
of the house. It descends only when it is cooler
than the air rising from the absorber. I'll bet
this arrangement is more efficient than feeding
the collector from the bottom of the living space
and heating the upper glazing to the maximum air
temperature. (Even if it isn't, I think it would
still be a worth avoiding collection system
dampers.)



Posted by nicksanspam on October 8, 2003, 11:29 am
 


Sounds good. The underside of the ceiling might have just enough
high-emissivity surface to keep the house warm on an average winter day,
with the rest low-e, eg foil-faced foamboard, so the fan is only required
on very cold days... Dissimilar heat losses on opposite house walls would
also make a convective loop to circulate room air under the ceiling.


Sounds very nice, in dense urban areas or flood plains, with parking
beneath the living space and a fast DC winch with a platform disk on
a fireman's pole and a counterweight, vs stairs :-)


An untratified store seems cheaper and smaller, with less heat loss through
its smaller insulated wall surfaces. The collector might be larger, but heat
storage can be more expensive than simple collection. Stratification seems
to make more sense with low-flow collectors or a backup system that uses
lots of fuel.


Sounds like the attic isn't storing much heat.


I wonder if there's a low-e ceiling...


I see "130 F" in Shurcliff's Super Solar House book. And a note:

  This chapter is written as if the house were complete. This makes
  the account shorter and simpler. In fact, as of May 1983, some details
  of construction and solar design were not complete. Some of the facts
  presented concerning design details are merely my best guesses as to
  what will become reality...


I would tend to agree. We might explore this further, with some numbers.
Then again, the outer sunspace glazing stays cooler, in the case of a solar
closet or shelfbox, or a transpired mesh to the south of the sunspace glazing
with 70 F room air between the mesh and the glazing and south to north airflow
through the mesh. Norman also used this kind of collection, with dark window
screen tilted south behind the south glazed non-window parts of some houses,
saying it decreased reradiation loss through the glazing.

Nick


Posted by David Delaney on October 8, 2003, 4:08 pm
 On 8 Oct 2003 07:29:20 -0400,
nicksanspam@ece.vill.edu wrote:


Sometimes an unstratified store is better.

But where the store can stratify well, a small
amount of heat collected at high temperature will
be *stored* at high temperature, and remain
available for use even if most of the store is
cold. If the store can not stratify, a small
amount of heat collected at high temperature when
the store is cold will be degraded to low
temperature, and rendered unavailable for use.

Also, consider the case of a thermal mass above a
convective hot air collector. If the air flow is
arranged so that the hot air heats the bottom of
the mass preferentially (enters only there), the
temperature of the mass will not be stratified.
The mass will not accept energy from the collector
above the average temperature of the mass. Or, if
the air flow is arranged so that the hot air heats
the top of the mass first (enters only there), the
temperature of the mass will be stratified, but
again the mass will not accept air from the
collector above the average temperature of the
mass. Or finally, if the air flow is arranged so
that the air rises beside a thermal mass which is
permeable on the side, the air will enter the mass
at the level at which its temperature equals the
temperature of the air in the mass. Not only will
the mass be well stratified, but it will accept
air from the collector at any temperature above
the temperature of the coldest part of the mass.

To exploit the last case we have to design a store
that is permeable on at least one side, has enough
internal surface area, and does not weigh too
much. A wall of gabions full of rocks would meet
the first two of these requirements, but water
would be a lot lighter if we could provide enough
surface area per lb.


In the Cliff house, the attic storage rate is low
because of the low mass/glass surface ratio, as
you have said. But the attic store is well
stratified, because air is continually extracted
from the attic store at the middle height of the
store, to be pushed down to the house and
under-slab rock bin (the main heat store). The
lower part of the upper store is continually
replenished by relatively cool air from the top of
the living space.

If there is to be only an upper store, it must
have have a higher mass/glass surface ratio than
the Cliff house.

The temperature of the air at the top of the
living space is limited by the under-floor slab
and the controlled fans.


The descending air is much cooler than 130F
(because it never exceeds the temperature of the
top of the living space.)


Yes. One of the reasons that I am approaching this
very carefully. (Shurcliff's detailed description
of Saunders's cliff house on the web:
<http://www.geocities.com/davidmdelaney/Solar-thermal-energy-for-housing.html> ,
or Google saunders cliff house.)

David

Posted by Eric Jacobsen on October 8, 2003, 10:07 pm
 
<http://www.geocities.com/davidmdelaney/Solar-thermal-energy-for-housing.htm
l>,

wow, cool stuff, thanks for your link.  is there anything out there with
details of how the house performed post-1983?

Have you assuaged your worry about mold growth in the rock-bin?

Eric




Posted by David Delaney on October 8, 2003, 10:52 pm
 On Wed, 8 Oct 2003 16:07:40 -0600, "Eric Jacobsen"


I tried for some time to learn about the life of
the Cliff House. I even located a current address
in Weston Mass. (the location of Cliff House) of a
person of the same name as the first owner, who
was also the builder. I wrote a cold snail mail to
the address requesting a conversation on a collect
call or any mode convenient for him, but never
heard back.

I currently do not plan to use a sub-floor rock
bin or any other than an attic store. If I were
planning to use a rock bin I would not be at all
worried about mold growth provided I did not
intend to use the rock bin for summer cooling.
When used for heating only, the RH of the air in
the rock bin would always be too low for mold
growth.

David Delaney, Ottawa

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